More importantly, we replicated our earlier analyses
suggesting that accuracy increased with conidence. In partic-
ular, we found that identiication of the culprit when present
in the lineup was close to 100% at the highest level of witness
conidence. In other words, when viewing lineups at the Robbery
Division of the Houston Police Department, if an eyewitness
identiied the suspect with high conidence, that person was
almost always the culprit.This result does not completely depend on our 35% base
rate estimate. We also estimated accuracy based on different
estimates of the proportion of culprit-present lineups(25–75%).
Identiication accuracy was unaffected and remained close to
100% when witnesses were highly conident.
Finally, we used the mathematical model to compare memory
strength between simultaneous and sequential lineups.Unlike
many laboratory studies, we foundthat memory strength was
always greater for simultaneous lineups than for sequential lineups.
The results of our study are important for two reasons. First,
we were able to investigate eyewitness reliability for crimesconducted in the real-world rather for simulated crimes in labo-
ratory settings. Second, in contrast to the conclusions reached
from many laboratory-based simulations, we found that eyewit-
ness identiications are highly accurate when they have high
conidence in their identiication.
Furthermore, and again in contrast to the conclusions reached
from many laboratory-based simulations, we found that a simul-
taneous lineup led to higher levels of memory strength than a
sequential lineup.
How do our results square with the
Innocence Project, which found that
a high number of false convictions
were based on unreliable eyewitness
identiications? The answer to this
question lies in where and when coni-
dence is measured.
Our results support the view that
conidence expressed at the time of
identiication from a fair lineup is a
reliable index of accuracy. However,
conidence can increase over time as
more information is learned by the
witness, reducing its usefulness as an
index of accuracy.
This effect has been known for a
long time. In a well-known psycho-
logical study conducted in the 1950s,
people were asked to judge whether
two straight lines were continuous or slightly disjointed. Most
people were not initially conident in their original decision, but
when surrounded by other people who all appeared very coni-
dent in one decision or the other (because they were coached
by the experimenter to say this), most people increased their
stated conidence in that decision even when the evidence of
their own eyes stayed exactly the same.
The story for lineups is much the same – only initial coni-
dence counts.
John Dunn is Professor of Psychology atThe University of Adelaide, and Chair of the
Australian Psychology Accreditation Council.20 | MAY 2016
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